The basic concept of filling containers by dispensing materials from a hopper using a rotary feed mechanism is well known. See, for example, U.S. Pat. Nos. Re. 23,888 and Re. 24,079. Apparatus such as that shown in these patents can be used for volumetric filling of free-flowing and non-free-flowing granular, powdered, flaked or paste material. Typically, the feed mechanism is positioned in an opening in the bottom of a vertically-disposed conical hopper and consists of either an auger or a pump. The auger, pump rotor, or other rotational member is driven by a prime mover, such as an electric motor, through a clutch-brake mechanism which connects the driving shaft of the motor to the driven shaft of the rotational member. The clutch-brake mechanism is controlled to rotate the driven shaft for a pre-selected number of revolutions by a device which counts the number of revolutions. This is a relatively accurate way of volumetrically dispensing material since the amount of material dispensed by each revolution of the auger or pump can be accurately determined. For example, for each revolution of an auger of known pitch and diameter, the volume of material dispensed from its discharge end can be determined. By appropriate control, the auger can be made to run through sequential cycles of a predetermined number of turns. During each cycle, therefore, a predetermined volume of material is discharged into a container positioned by mechanized packaging devices between the discharge end of the feed mechanism. Mechanized packaging line devices for sequentially positioning containers made of paper, metal, plastic or glass are well known.
Since each revolution of the feed mechanism dispenses a known amount of material, it follows that the number of revolutions is a measure of the volume of material that has been dispensed. There are two methods for determining the number of revolutions. The first method is to directly count the number of revolutions. The second method is to measure the time period over which the feed mechanism is being driven at a constant speed. In known apparatus, devices for counting the number of revolutions include counters directly linked by gearing the output side of the clutch-brake mechanism mentioned above, and shaft encoders directly or indirectly coupled to the driven shaft which generate a given number of pulses for each complete revolution of the driven shaft. When the correct count is reached, the driven shaft is disengaged from the driving shaft and braked by the clutch-brake mechanism. Although such mechanisms are manufactured with precision and assembled with rigorous quality monitoring, in some cases inherent errors result in a repetitive accuracy of performance less than desired.
The timed method of controlling the number of revolutions is less accurate than the count method, although in certain cases the timed method of controlling the number of revolutions may yield acceptable accuracy.
One factor which contributes to the inherent inaccuracies in the direct counting method of determining the number of shaft revolutions is what may be termed shaft "coast". It is known that, due to the inertia of a rotating shaft and practical limits on the braking system, a rotating shaft will continue to rotate for a fraction of a revolution or even several revolutions after the brake is applied before coming to a complete stop. This additional, unwanted rotation of the shaft after the brake is applied and before it comes to a complete stop is referred to as "coast". Obviously, as an auger shaft coasts beyond the desired number of turns it continues to dispense material from the hopper. This results in over-filling of the containers, with concomitant spilling, waste and loss of time and money to the packer.
It is an object of the present invention to compensate for the coast inherent in any filling machine so that a more accurate fill is obtained.
In addition to compensating for coast, there is another aspect to the invention. As noted above, known filling machines operate in a volumetric mode. That is, for an auger of known pitch and diameter, each revolution of the auger dispenses a given volume. However, in many instances, the material being filled into the container is ultimately sold to the consumer by weight, not volume. Thus, in order to fill a one-pound coffee can with one pound of coffee, for example, the filling machine must dispense a particular volume of coffee which will have a weight of one pound. Obviously, the weight of the material dispensed is equal to the product of the density of the material times the volume dispensed. Variations in density, due to factors such as temperature, humidity or other factors, will result in different weights of material for a given volume. In order for an operator to be sure that he is consistently filling containers to the proper weight, he must engage in a lengthy, time-consuming and potentially inaccurate process of finding the volume which gives him the desired weight for a particular product run. Typically, this necessitates a large number of trial cycles in which the operator fills a container with a volume which he estimates will give him the desired weight. He then weighs the container, and adjusts the volume delivered depending upon whether the weight is high or low. Depending upon the operator's skill and the particular product and ambient conditions, this may take a large number of trials.
It is another object of the invention to eliminate the need for a large number of trial fill cycles when setting up a filler machine and to permit the number of auger revolutions required to dispense a given weight in a single trial fill operation.